MIMO is considered essential for evolved universal terrestrial radio access (E-UTRA) to provide high data rate and increased system capacity for an orthogonal frequency division multiple access (OFDMA) downlink (DL). It is desirable to use MIMO for an SC-FDMA uplink (UL) for the same reasons. A significant improvement in data rates and throughput using MIMO precoding for SC-FDMA for the uplink has been shown. E-UTRA supports an instantaneous uplink peak data rate of 50 Mb/s within a 20 MHz uplink spectrum allocation (2.5 bps/Hz) assuming a 16-QAM modulation.
When practical coding rates (e.g. 1/2) are used, the instantaneous uplink peak data rate is much less than 50 Mb/s. To achieve this data rate while using practical coding rates, utilization of a MIMO configuration is necessary. It has also been noted that to achieve the highest throughput in uplink transmission, the use of precoding is a necessity. Using MIMO for an SC-FDMA uplink (UL) requires the use of at least two transmitters, one for each uplink MIMO antenna. An additional advantage to having two or more transmitters in the WTRU is the possibility of using beamforming to enhance multi-user MIMO, and also transmit diversity schemes such as Space Time (ST)/Frequency Decoding (FD).
The efficient feedback can reduce feedback overhead or improve performance. A potential feedback overhead reduction is obtainable when using Jacobi rotation for eigen-basis feedback. Additional overhead reduction is achievable using a differential feedback by an iterative approach for the Jacobi transform to track the delta of the eigen-basis and then provide feedback to the new eigen-basis.
It would be desirable to use differential feedback and iterative Jacobi rotation for potential feedback overhead reduction and performance improvement. Iterative Jacobi rotation-based feedback is a potential solution for a two or more transmit antenna MIMO proposal.